Direct-bonded optoelectronic interconnect for high-density integrated photonics

ABSTRACT

Direct-bonded optoelectronic interconnects for high-density integrated photonics are provided. A combined electrical and optical interconnect enables direct-bonding of fully-processed optoelectronic dies or wafers to wafers with optoelectronic driver circuitry. The photonic devices may be III-V semiconductor devices. Direct-bonding to silicon or silicon-on-insulator (SOI) wafers enables the integration of photonics with high-density CMOS and other microelectronics packages. Each bonding surface has an optical window to be coupled by direct-bonding. Coplanar electrical contacts lie to the outside, or may circumscribe the respective optical windows and are also direct-bonded across the interface using metal-to-metal direct-bonding, without interfering with the optical windows. Direct hybrid bonding can accomplish both optical and electrical bonding in one overall operation, to mass-produce mLED video displays. The adhesive-free dielectric-to-dielectric direct bonding and solder-free metal-to-metal direct bonding creates high-density electrical interconnects on the same bonding interface as the bonded optical interconnect. Known-good-dies may be used, which is not possible conventionally, and photolithography over their top surfaces can scale to high density.

RELATED APPLICATIONS

This patent application claims the benefit of priority to U.S.Provisional Patent Application No. 62/599,146, filed Dec. 15, 2017 andincorporated by reference herein in its entirety.

BACKGROUND

Silicon, as a good conductor of infrared light, has become important tooptoelectronics and provides many technical and economic advantages.Silicon photonics combines the advantages of photonics with thewidespread use of silicon in conventional CMOS manufacturing. Photonicsoffers high-performance communication, low power of operation, and smallsize and weight. CMOS offers volume production, low cost,miniaturization, and high integration. Silicon photonics thereforeprovides high integration, miniaturization, higher bandwidth, lowercost, and lower power of operation. Micro-optoelectronic integrationusing silicon photonics cuts the cost of optical links.

Compound semiconductors for optoelectronics and silicon photonicscombine an element from group III of the periodic table (e.g., In, Ga,Al) with an element from group V of the periodic table (e.g., As, P, Sb,N). This yields twelve different III-V compounds, but the mostcommercially useful of these are currently GaAs, InP, GaN, and GaP.

Silicon photonic circuits most often operate in the infrared at awavelength of 1550 nanometers, at which silicon becomes a good conduitfor transmission of the infrared optical beams. A top and bottomcladding of silicon dioxide (silica) on a waveguide structure made ofsilicon confines the infrared light within the silicon by total internalreflection (TIR) due to differences in the refraction indices of siliconand silicon dioxide, similar in some respects to how light is conductedin a fiber optic filament. Silicon photonic devices that use suchsilicon waveguides can be constructed by semiconductor fabricationtechniques previously used exclusively for microelectronics. Sincesilicon is already used as the substrate in most conventional integratedcircuits for microelectronics, hybrid devices in which the optical andelectronic components are integrated onto a single microchip can be madewith conventional semiconductor fabrication processes, sometimes evenwithout retooling.

Processes that fabricate photonic devices using silicon and silicondioxide can also utilize conventional silicon on insulator (SOI)techniques that are already well-known in microelectronics, providing aSOI waveguide layer on a wafer, to which optical dies such as LEDs,lasers, and photodetectors may be conventionally attached byless-than-ideal means.

Platforms based on silicon photonics that could foster highly integratedelectronic-photonic convergence face several obstacles. Due to opticalmode matching requirements, a thick transparent substrate, such assapphire or indium phosphide (InP) cannot conventionally be bonded ontoa silicon wafer. This is because the III-V compound semiconductors,while providing additional function over silicon, are usually fromdifferent sources with different base materials. So instead ofconventional bonding, flip-chip and/or die-to-wafer (D2 W)interconnection and packaging techniques are conventionally used to bondsuch optical dies to a silicon wafer. Die-to-wafer bonding is requiredfor integrating dies with III-V compound semiconductors onto the siliconchip, but the bulky solder interconnects characteristic of thesetechniques pose an obstacle to the optical path. Options that use thesesolder interconnects and apply mirroring optics to compensate arecomplex and costly. So to avoid the solder interconnects, fabrication inconventional photonics usually bonds unprocessed photonic dies to thesilicon wafer, but then has to fabricate metal contacts of theoptoelectronic devices on the dies in a retroactive front-end step afterthe dies have already been bonded to the wafer.

Because the dies with the III-V compound semiconductors areconventionally not fully processed before bonding to the silicon wafer,the process cannot be optimized by selecting known-good dies, and thusfront-end processes have to be performed after the dies have alreadybeen bonded to the wafer. Photolithography over the topographic surfaceof the dies, after die-to-wafer bonding, has limited precision andcannot scale to high density.

SUMMARY

Direct-bonded optoelectronic interconnects for high-density integratedphotonics are provided. A combined electrical and optical interconnectenables direct-bonding of fully-processed optoelectronic dies that haveIII-V semiconductor devices aboard to surfaces, such as the surfaces ofsilicon, silicon-on-insulator (SOI) wafers, quartz and so forth,enabling the integration of photonics with high-density CMOS IC drivercircuitry in microelectronics packages. The direct-bonded optoelectronicinterconnect may also be used in other wafer level production processesthat bond organic LEDs (OLEDs) or quantum dot LEDs on a first wafer toCMOS driver circuitry on a second wafer. The example direct-bondedoptoelectronic interconnect may also be used to direct-bond diced LEDchips to wafers, or to other chips.

Each bonding surface of an LED wafer or chip, and a CMOS wafer or chipto be direct-bonded, has an optical window to be coupled bydirect-bonding. Electrical contacts coplanar with the optical window arealso direct-bonded across the same bonding interface usingmetal-to-metal direct-bonding. Direct hybrid bonding can accomplish boththe optical bonding and the electrical bonding in one overall operation.Adhesive-free dielectric-to-dielectric direct bonding and solder-freemetal-to-metal direct bonding create high-density electricalinterconnects on the same bonding interface as the bonded opticalinterconnect. Since the optoelectronic dies can be fully-processed fromthe outset, known-good-dies may be used, which is not possibleconventionally. Since the optoelectronic dies begin as fully-processedcomponents, photolithography over their top surfaces can scale to highdensity.

The example optoelectronic interconnect may be used to constructphotonic devices, including but not limited to photonic integratedcircuits (PICs), also known as integrated optical circuits, and planarlightwave circuits (PLCs). In addition, the optoelectronic interconnectmay used in the fabrication of photonic devices for fiber-opticcommunications, optical computing, for medical applications includingminimally invasive scanner probes, for aeronautic and automotiveapplications, such as optical sensors for shape-sensing changes inflexing parts, and optical metrology, for example. The exampleoptoelectronic interconnect may be used to fabricate photonic devicesusing wafer level processes and microelectronic packaging techniques.

This summary is not intended to identify key or essential features ofthe claimed subject matter, nor is it intended to be used as an aid inlimiting the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the disclosure will hereafter be described withreference to the accompanying drawings, wherein like reference numeralsdenote like elements. It should be understood, however, that theaccompanying figures illustrate the various implementations describedherein and are not meant to limit the scope of various technologiesdescribed herein.

FIG. 1 is a diagram of optoelectronic dies with III-V semiconductorcomponents aboard and with completed metallization and finishedelectrodes being direct-bonded to a wafer to make photonic devicesintegrated with high-density microelectronics.

FIG. 2 is a side view diagram of an example optoelectronic interconnectimplemented by direct-bonding in a single direct-bonding plane.

FIG. 3 is a top view diagram of example respective direct-bonding planesof an example optoelectronic die and an example silicon orsilicon-on-insulator (SOI) wafer to be direct-bonded together to make anexample optoelectronic interconnect.

FIG. 4 is a diagram of an example optoelectronic interconnect in whichthe first electrical contact of the photonic device and the secondelectrical contact of the photonic device are each single metal pads tobe direct-bonded.

FIG. 5 shows an implementation of the example optoelectronicinterconnect in which the first electrical contact of the photonicdevice and the second electrical contact of the photonic device are eachone or more metal pads on two or more sides outside of the optical areasto be direct-bonded.

FIG. 6 shows an example photonic device, in which photonic devices, suchas LEDs, mLEDs, or laser sources are arrayed on a wafer using theexample optoelectronic interconnect.

FIG. 7 shows another example photonic device, in which photonic devices,such as LEDs, mLEDs, or laser sources are arrayed on a wafer using theexample optoelectronic interconnect.

FIG. 8 is a flow diagram of an example method of creating planar bondinginterfaces suitable for direct-bonding a die that includes a photonicdevice, such as a photonic device utilizing a III-V semiconductorcompound to a wafer, such as a silicon or SOI wafer, to form anoptoelectronic interconnect for high-density integrated photonics.

FIG. 9 is a flow diagram of another example method of bonding a die thatincludes a photonic device utilizing a III-V semiconductor compound to asilicon or SOI wafer to form an optoelectronic interconnect forhigh-density integrated photonics.

DESCRIPTION

This disclosure describes direct-bonded optoelectronic interconnects forhigh-density integrated photonics. A combined electrical and opticalinterconnect enables direct-bonding of fully-processed optoelectronicdies or wafers that include III-V semiconductor devices, OLEDs, orquantum dot LEDs to silicon, or silicon-on-insulator (SOI) wafers,particularly to CMOS wafers carrying IC driver circuitry, with orwithout built in silicon or other optical waveguides. The exampledirect-bonded optoelectronic interconnect enables the integration ofphotonics with cutting-edge production techniques used to makehigh-density CMOS and other microelectronics packages.

In this description, the term LED for “light-emitting-diode” alsoencompasses microLEDs and the various types of LEDs, such asphosphor-based LEDs, III-V semiconductor LEDs, OLEDS, quantum dot LEDs,and so forth.

Wafers used in the example processes may be silicon orsilicon-on-insulator (SOI) wafers or may be made of other materials,such as quartz, polymer, and other, and may contain a silicon waveguideor other waveguide utilizing infrared light, for example. The exampleelectrical and optical interconnect described herein is not limited tosilicon-on-insulator (SOI) wafers, but SOI wafers are used as a workingexample.

First and second planar bonding surfaces of the die(s) and wafer to bebonded are made flat enough for a direct-bonding process. The respectiveoptical windows of die and wafer are direct-bonded to each other acrossthe bonding interface by a dielectric-to-dielectric (or oxide-oxide)direct-bonding process, for example. The respective coplanar metalelectrical contacts are also direct-bonded to each other across the samebonding interface using a metal-to-metal direct-bonding process. Whendirect hybrid bonding (DBI® for example) is utilized, the nonmetaldirect-bonding of the respective optical windows occurs first (InvensasInc., a subsidiary of Xperi Corp., San Jose, Calif.). Then in anannealing step of the direct hybrid bonding operation, the complementaryelectrical contacts on opposing sides of the bonding interface aredirect-bonded together forming metal-to-metal bonds. The nonmetaldirect-bonding and then the metal direct-bonding results in adirect-bonded optoelectronic interconnect between dies bearing photonicIII-V semiconductor devices on one side, and a silicon or SOI waferbearing optoelectronic circuitry on the other side. The photonic devicesmay be lasers, photodetectors, optical diodes, LEDs, microLEDs, and soforth. LEDs are described herein, as a working example for the sake ofdescription.

In an implementation, matching metal contacts on either side of thebonding interface between die and wafer, or between wafer and wafer, arein a different bonding area than the optical path provided by theoptical areas to be interconnected by direct bonding, while remainingcoplanar with the optical areas so that there is only one planar bondinginterface for both optical and electrical interconnects created in onebonding operation. In an implementation, the electrical contacts to bedirect-bonded between surfaces are coplanar with, and lie to the outsideof the respective optical areas of the surfaces being direct-bondedtogether. In another implementation, the electrical contacts to bedirect-bonded across the optoelectronic interconnect are coplanar with,and circumscribe, at least in part, the respective optical areas beingdirect-bonded together. The combined optical and electrical interconnectenables high-density integration of photonics into microelectronicpackages, because the adhesive-free dielectric-to-dielectric bonding andthe solder-free metal-to-metal bonding employed can create high-densityelectrical interconnects on the same bonding interface as the bondedoptical interconnect, and can be scaled to high density.

FIG. 1 shows optoelectronic dies 100, such as fully-processedoptoelectronic dies 100, with III-V semiconductor optical devices aboardand with completed metallization and finished electrodes, for example,being bonded to an example silicon wafer or to an examplesilicon-on-insulator (SOI) wafer 102 using die-to-wafer (D2 W)techniques. The configuration of electrical contacts between die 100 andwafer 102, and the configuration of optical areas also to beinterconnected between die 100 and wafer 102, enable the conductivecontacts of the dies 100 to be metal-to-metal direct-bonded, withoutsolder, while the dielectric surfaces of the optical areas are alsodirect bonded between die 100 and wafer 102 without adhesives. Thesolder-free process and absence of bulk solder enable formation ofhigh-density electrical interconnects on the same planar bondinginterface as the optical interconnect that is being created. Moreover,finished optoelectronic dies 100 can be used in the die-to-wafer bondingoperation. Although the finished optical devices 100 are shown to bebonded to silicon or a SOI wafer 102 in FIG. 1, a finished opticaldevice wafer can alternatively be hybrid direct-bonded to silicon,glass, quartz or SOI wafer.

In a wafer-to-wafer (W2 W) process, LEDs 104 or microLEDs (mLEDs) 104may be formed or reconstituted on a wafer 106 or reconstituted wafer,which is then direct-bonded to another wafer 102 using the exampleoptoelectronic interconnect described herein. The wafer 102 being bondedto can possess CMOS driver circuitry, for example, with opticalwaveguides.

FIG. 2 shows an implementation of an example combined electrical andoptical (“optoelectronic”) interconnect 200 for high-density integratedphotonics. In an implementation, an example die 100 includes anoptoelectronic device 202 and an optical coupling area 204 of the die100 in optical communication with the optoelectronic device 202. The die100 may be a fully processed III-V die of a laser, photodiode, LED, andso forth. The example die 100 has a coupling plane 206 (also shown inFIG. 3) for optically and electrically coupling with a complementarycoupling plane 208 of the wafer 102, such as a silicon-on-insulator(SOI) wafer, silicon, glass or other wafer. A segment of the couplingplane 206 of the die 100 contains the optical coupling area 204 of thedie 100. Example direct-bonded LED arrays and applications are describedin U.S. patent application Ser. No. 15/919,570 to Tao et al., filed Mar.13, 2018 and incorporated by reference herein in its entirety. The mLEDarrays in the above Tao et al. reference utilize the direct-bondedoptoelectronic interconnect 200 described herein, for example.

The coupling planes 206 & 208 of the die 100 and wafer 102,respectively, are provided a high degree of physical flatness suitablefor direct bonding of metals and nonmetals in the bonding planes 206 &208. This flatness may be achieve by manufacture or by polishing, suchas by chemical mechanical planarization (CMP), for example.

A first electrical contact 212 of the optoelectronic device 202 isdisposed outside the perimeter of the optical coupling area 204, withinthe coupling plane 206 of the die 100. The first electrical contact 212lies outside of, and in some cases may fully or at least partiallysurround the outside perimeter of the optical coupling area 204 in thecoupling plane 206 of the die 100. A second electrical contact 214 ofthe optoelectronic device 202 is also disposed outside the perimeter ofthe optical coupling area 204, and in some cases may also be disposedoutside a perimeter of the first electrical contact 212, in the couplingplane 206 of the die 100. When the second electrical contact 214 issituated past the outside perimeter of the first electrical contact 212,the second electrical contact 214 may at least partially surround thefirst electrical contact 212. In an implementation, the first (“inner”)electrical contact 212 completely surrounds the optical coupling area204 with an unbroken perimeter of metal trace in the coupling plane 206of the die 100. In another implementation, as shown later in FIGS. 4-5,the first electrical contact 212 and the second electrical contact 214may be pads or point-of-contact connectors for direct bonding that aresimply located in a different region of the bonding interface than theoptical bonding region 204.

The first electrical contact 212 of the die 100 (or optical devicewafer) is also configured to match a complementary electrical contact222 on the wafer 102 being bonded to, outside a region or a perimeter ofa complementary optical coupling area 216 of the wafer 102. This placesboth complementary electrical contacts 212 & 222 outside the perimeteror the optical footprint of a silicon waveguide 218 in or under theoptical coupling area 216 of the wafer 102.

In the shown example, from the standpoint of the planar bottom waferside 208 of the bonding interface 200, instances of the example die 100are capable of optically and electrically coupling with the wafer 102upon joining respective coupling planes 206 & 208 of the dies 100 andwafer 102. The optical coupling area 216 of the wafer 102 occupies aflat segment of the coupling plane 208 of the wafer 102. For eachdie-to-wafer bonding site, the wafer 102 has a respective siliconwaveguide 218 in optical communication with the optical coupling area216 of the wafer 102, that is, above the silicon waveguide 218.

The wafer 102 has an optoelectronic circuit 220 & 220′ or otherelectrical circuit, to be connected to the electronics of the die 100across the bonding interface 200. Although the optoelectronic circuit220 & 220′ are depicted to be on the bonding surface 208, they may beunderneath or embedded into or under the bonding surface 208. A firstelectrical contact 222 of the optoelectronic circuit 220 of the wafer102 is complementary in planar geometric profile in the bonding plane208 with the first electrical contact 212 in the coupling plane 206 ofthe die 100 (see FIG. 3, also). The first complementary electricalcontact 222 of the wafer 102 is co-disposed in the coupling plane 208 ofthe wafer 102 and disposed outside a perimeter of the optical couplingarea 216 of the wafer 102.

In the shown implementation, a second electrical contact 224 of theoptoelectronic circuit 220 of the wafer 102 is disposed outside aperimeter of the first electrical contact 222 of the wafer 102, and isalso disposed in the flat coupling plane 208 of the wafer 102. Thesecond electrical contact 222 is complementary in flat profile to thecorresponding second electrical contact 214 of the die 100, to which itwill bond via metal-to-metal direct bonding.

Electrical routing paths (leads, conductive lines, traces) from theoptoelectronic circuit 220 of the wafer 102 to the first and secondcomplementary electrical contacts 222 & 224 of the wafer 102 may also bewithin or just under the coupling plane 208 of the wafer 102, asintroduced above.

The optical coupling area 216 of the wafer 102 may include at least agrating surface 226 for an optical mode-match coupling between theoptics of the die 100 and the silicon waveguide 218 of the wafer 102. Inan implementation, the grating surface 226 may be less than 10 microns(p) wide for single mode infrared transmission in the silicon waveguide218.

As described above, the die 100 has fully-processed electrodes for theoptoelectronic device 202 aboard the die 100, and fully-processed firstand second electrical contacts 212 & 214 for making the electricalinterconnect with the corresponding electrical contacts 222 & 224 on aplanar bonding interface 208 of the wafer 102. When the coupling plane206 of the die 100 and the coupling plane 208 of the wafer 102 arejoined, optical coupling and metal-to-metal electrical coupling occur inthe same bonding operation at the combined coupling planes 206 & 208being joined (“coupled plane” or “optoelectronic interconnect” 200).

A direct hybrid bonding operation, such as example DBI® direct hybridbonding, for example, may be used to accomplish thedielectric-to-dielectric direct bonding (e.g., oxide-to-oxide directbonding) of nonmetals that make up the surfaces of the complementaryoptical areas 204 & 216 of the die 100 and wafer 102. An annealing stepof the same example direct hybrid bonding process also direct-bonds therespective metal electrodes together, and strengthens all direct bondscreated in the example direct hybrid bonding process.

The coupled plane 200 at the bonding interface 206 & 208 perfects anoptical couple between the optical coupling area 204 of the die 100 andthe optical coupling area 216 of the wafer 102, mated in the joinedcoupling plane 200. The coupled plane 200 at the bonding interface alsoincludes the metal-to-metal direct-bond between the first electricalcontact 212 of the die 100 and the complementary electrical contact 222of the wafer 102, and likewise includes the metal-to-metal direct-bondbetween the second electrical contact 214 of the die 100 and thecomplementary electrical contact 224 of the wafer 102.

A transparent conductive oxide (TCO) 228 or other similar film may beadded between the III-V compound semiconductor (or optical device) 202and the silicon waveguide 218 to enhance electrical conductivity into aIII-V compound semiconductor 202, for example, or to enhance auniformity of the electrical conductivity into a III-V compoundsemiconductor 202, when needed.

In an implementation, reflection loss may be reduced by roughening abottom surface of the III-V compound semiconductor or optical device 202by etching, for example. In another technique for reducing reflectionloss, a selected dielectric material between the bottom surface of theIII-V compound semiconductor 202 and the silicon waveguide 218 may beused to reduce a reflection loss between the III-V compoundsemiconductor 202 and the silicon waveguide 218. In an implementation,the dielectric material to be used has a refractive index approximatelyequal to the square root of the index of refraction of the silicon 218multiplied by the index of refraction of the III-V compoundsemiconductor material 202. In another implementation, the dielectricmaterial has a refractive index that is in the range between the indexof refraction of the silicon 218 and the index of refraction of theIII-V compound semiconductor 202.

Accordingly, some common indices of refraction for dielectrics andsemiconductors, that can also be used for reduction of reflection lossin the example optoelectronic interconnect are:

Silicon n = 3.9766 SiO₂ n = 1.4585 ITO (Indium tin oxide) n = 1.858 GaNn = 2.3991 InP n = 3.5896 GaAs n = 3.9476 TiO₂ n = 2.6142

As an example, TiO₂ may be used as the intervening dielectric materialto reduce reflection loss. Dielectric materials such as aluminum dopedzinc oxide (AZO) and gallium doped zinc oxide (ZNO) may also be used,depending on the III-V compound semiconductor 202 that is present. It isalso likely that the optical interconnect is between silicon oxide andGaN as silicon oxide may act as the optical waveguide

The optical part of the optoelectronic interconnect 200 can also beoptimized by configuring an optical thickness between the bottom surfaceof the III-V compound semiconductor 202 and a top surface of the siliconwaveguide 218. The thickness can be an odd multiple of one-quarter ofthe wavelength of the operative light, such as infrared light at 1550nm, that is used in each photonic device being formed by joining theoptoelectronic die 100 and the wafer 102.

Depending on the thickness of a substrate 230 of the die 100 to bebonded to a wafer 102, layers of the substrate 230 may be removed bylaser liftoff, grinding, etching, and so forth, to thin the dies 100being bonded. Then, a reflective layer, metal, or distributed Braggreflector (DBR) 232, for example, may be added on top of theoptoelectronic device 202 of the die 100 to keep the light contained andfavorably reflected into the optoelectronic devices 202 on the dies 100.

FIG. 3 shows top views (or bottom views) of the example bonding planes206 & 208 of the respective die 100 and wafer 102 forming the exampleoptoelectronic interconnect 200. FIG. 2, by comparison, shows a sideview. This configuration of the electrodes 212 & 222 and 214 & 224 to bedirect-bonded together, are just one example configuration. Otherexample configurations are shown in FIGS. 4-5.

In FIG. 3, in an example embodiment, the first coupling plane 206 formedon a side of the die 100 has the first optical bonding area 204 formedin the coupling plane 206, the first electrical contact 212 around theoutside perimeter of the first optical window 204, which is alsodisposed in the coupling plane 206 of the die 100, and has the secondelectrical contact 214 around the outside perimeter of the first “inner”electrical contact 212, all of these disposed in the coupling plane 206of the die 100.

The wafer-side bonding plane 208 of the electrical and opticalinterconnect 200 for high-density integrated photonics includes thewafer-side optical window 216 in the coupling plane 208, the firstelectrical contact 222 of the wafer 102 outside a perimeter of theoptical window 216, the second electrical contact 224 of the wafer 102outside a perimeter of the first electrical contact 222, and electricalleads 302 & 304 connected respectively to the first electrical contact222 and the second electrical contact 224, all of these disposed in thecoupling plane 208 of the wafer 102.

In an implementation, the second complementary electrical contact 224 ofthe optoelectronic circuit 220 of the wafer 102 is an open-loop or otherdiscontinuous flat shape within the coupling plane 208 of the wafer 102,and has a gap 300 in its open-loop or discontinuous form foraccommodating the electrical routing 302 from the circuit 220 to thefirst complementary electrical contact 222 within the coupling plane 208of the wafer 102. The gap 300 allows the second electrical contact to224 remain electrically insulated from the lead 302 or other conductiveline leading to the first electrical contact 222 of the optoelectroniccircuit 220.

The first electrical contact 212 of the die 100 and the firstcomplementary electrical contact 222 of the wafer 102 may each be aconductive line or trace or ring in the form of a square, rectangle,circle, or oval, for example, surrounding respective first and secondoptical windows 204 & 216.

The electrical and optical interconnect 200 for high-density integratedphotonics, when joined, has a dielectric-to-dielectric direct-bondedoptical interconnect between the (first) optical window 204 of the die100 and the (second) optical window 216 of the wafer 102. The electricaland optical interconnect 200 also has solder-free metal-to-metaldirect-bonded electrical interconnects between the first and secondelectrical contacts 212 & 214 of the die 100 and their complementaryfirst and second electrical contacts 222 & 224 of the wafer. Thedirect-bonding of both the optical areas 204 & 216 and the respectiveelectrical contacts 212 & 222, and 214 & 224 creates a complete bondinginterface 200 that creates the capacity for high-density optoelectronicinterconnects 200 via the joined coupling planes 206 & 208 between thedie 100 and the wafer 102.

Although the electrical contacts 212, 214, 222 & 224 are shown asexposed to the surface in FIG. 3, in one scenario only portions of thecontacts in the form of small pads are exposed and actually bonded. Notall CMP processes can planarize bonding surfaces with exposed metalloading in the form of rings as depicted in FIG. 3. Instead, in someimplementations, a more uniformly exposed metal loading (distributedpads) may be more suitable from an optimized CMP process.

Although the electrical contacts 212, 214, 222 & 224 are shown as aconductive line or trace formed in a ring, a square, a rectangle, acircle, or an oval shape, it is also possible that each of theelectrical contacts is in the form of only one (or more) pads, notnecessarily circumscribing the optical windows 204 or 206. Also, eachsuch pad may be electrically connected to its die 100 by athrough-conducting via. Examples of pad-bonding implementations areshown in FIGS. 4-5.

After the direct-bonded optoelectronic interconnects are formed betweendies 100 and wafer 102, the wafer 102 and its bonded dies 100, may bediced or individuated into individual optoelectronic devices, or intogroups of optoelectronic devices. For some applications a wafer 102 withdirect-bonded bonded dies 100 may be left intact and undiced, with anarray of the optoelectronic devices on relatively large sections of thewafer 102, for example, or on the entire wafer 102.

FIG. 4 shows an implementation of the example optoelectronicinterconnect 200 in which the first electrical contact 212 of thephotonic device 100 and the second electrical contact 214 of thephotonic device 100 are each single metal pads, polished and preparedfor direct metal-to-metal bonding with complementary pads 222 and 224 onthe surface 208 of the wafer 102 being direct bonded to. The contacts212 & 214 to be direct-bonded are both off to one side of the opticalareas 204 & 216, in a different direct-bonding area that does notinterfere with the direct-bonding of the optical areas 204 & 216. Theindividual bonding pads 212 & 214, or contacts, may be single instancesof respective pads (left) or multiple redundant instances of pads foreach lead or line (right), for bonding reliability. Multiple pads(right) may also be used when the photonic device has more than twoleads to be connected across the optoelectronic interconnect 200.

Traces or conductive lines 220 & 220′ coupling the bonding pads 222 &224 to a circuit, such as a LED driver circuit, of the wafer 102 beingbonded to are usually embedded or disposed below the bonding surface 208itself.

FIG. 5 shows an implementation of the example optoelectronicinterconnect 200 in which the first electrical contact 212 of thephotonic device 100 and the second electrical contact 214 of thephotonic device 100 are each metal pads, polished and prepared fordirect metal-to-metal bonding. Complementary pads 222 and 224 are on thesurface 208 of the wafer 102 being direct-bonded to. In thisconfiguration, the contacts 212 & 214 to be direct-bonded are on two ormore sides outside of the optical areas 204 & 216 to be direct-bonded,in one or more different direct-bonding areas that do not interfere withthe light path or with the direct-bonding between surfaces of theoptical areas 204 & 216. The individual bonding pads 212 & 214, orcontacts, may be single instances or respective pads (left), or may bemultiple redundant instances (right) of pads for each line or lead, forbonding reliability, if one of the redundant pads bonds weakly, forexample. Multiple pads (right) may also be used when the photonic devicehas more than two types of leads to be connected across theoptoelectronic interconnect 200.

Traces or conductive lines 220 & 220′ coupling the bonding pads 222 &224 to a circuit, such as a LED driver circuit, of the wafer 102 beingbonded to are usually embedded or disposed below the bonding surface 208itself.

FIG. 6 shows an example apparatus 600, in which photonic devices, suchas an array of LEDs, mLEDs, or laser sources are created or arrayed on awafer 602 or a reconstituted wafer to make the photonic device. Thesecond wafer 102 being bonded to may have electronic circuitry, such asCMOS driver circuitry to be connected to the photonic devices on thefirst wafer 602 by direct-bonding of electrical contacts 212 & 214between the two wafers 602 & 102 across the flat, optoelectronicinterface (206 & 208 joined by direct-bonding). To form theoptoelectronic interconnect, the two surfaces 206 & 208 of theoptoelectronic interface are flattened with CMP or other techniques forachieving ultra-flat direct-bonding surfaces. The surfaces 206 & 208being direct-bonded may also include respective optical bonding areas206 & 216. The second wafer 102, in addition to electronic drivercircuitry, may also contain photonic circuits (light paths), into whichlight is injected or illuminated through waveguides 218 beingdirect-bonded to the optical areas 204 of LEDs 100 or other photonicdevices.

Direct hybrid bonding, such as DBI® brand hybrid bonding, createsdirect-bonds between the nonmetallic (e.g., SiO₂) optical areas 204 &216, and in the same overall operation creates direct-bonds between themetallic electrical contacts 212 & 214 across the same optoelectronicinterface 206 & 208 to create wafer-to-wafer optoelectronicinterconnects at each photonic device.

FIG. 7 shows another example apparatus 700, in which photonic devices,such as LEDs, mLEDs, or laser sources are arrayed on a wafer 702. Thesecond wafer 704 being bonded to, may have electronic circuitry, such asCMOS driver circuitry to be connected to the photonic devices on thefirst wafer 702 by direct-bonding of electrical contacts 706 & 708between the two wafers 702 & 704 across the flat direct-bondinginterface (710 joined to 712).

The two wafers 702 & 704 of the example apparatus 700 may bedirect-bonded with a direct hybrid bonding process, such as DBI® branddirect hybrid bonding, in which both non-metals 714 and conductivemetals 714 are direct-bonded together in the same overall direct hybridbonding process. The nonmetals to be direct-bonded 714 may bedielectrics, and may or may not be optical areas for transmitting light.

In an implementation, the direct-bonding processes create a thin mLEDarray 700, in which the wafer 702 with the LED structures isdirect-bonded to a CMOS driver chip wafer 704.

To achieve the direct hybrid bonding, in an implementation, after theflat and activated surface 710 on the mLED device wafer 702 is formed,the CMOS wafer 704 is planarized with CMP or other means of obtaining anultra-flat surface, and plasma-activated 718, for example.

The two wafers 702 & 704 are then direct-bonded, between nonmetallicdielectric surfaces 714 and also between metallic conductors 716, duringan annealing phase, for example. After the nonmetallic dielectricsurfaces have directed bonded 714 on contact, the direct-bonding ofmetal conductors 716 can occur at an annealing temperature ofapproximately 100-200° C. to form a strong direct-bonded interconnect ofboth metals and nonmetals, to make the example mLED array 700.

Example Processes

FIG. 8 shows an example method 800 of creating a planar bondinginterface suitable for direct-bonding a die that includes a photonicdevice, such as a III-V semiconductor photonic device, to a wafer, suchas a silicon or SOI wafer, to form an optoelectronic interconnect forhigh-density integrated photonics. In some implementations, theoptoelectronic interconnect may direct-bond both electrical contactsacross an interface and may direct-bond an optical pathway across thesame interface. In the flow diagram of FIG. 8, operations of the examplemethod 800 are shown as individual blocks.

At block 802, a first optical window is created in a first planarbonding surface of a die, the die including a photonic device, such as asensor or a LED based on a III-V semiconductor compound.

At block 804, a first electrical contact of the photonic device of thedie is created in the first planar bonding surface, the first electricalcontact at least partially circumscribing the first optical window ofthe die.

At block 806, a second electrical contact of the photonic device of thedie is created in the first planar bonding surface, the secondelectrical contact at least partially circumscribing the firstelectrical contact.

At block 808, a second optical window in communication with a siliconwaveguide is created in a second planar bonding surface associated witha wafer.

At block 810, a first electrical contact of an optoelectronic circuit ofthe wafer is created in the second planar bonding surface, the firstelectrical contact at least partially circumscribing the second opticalwindow of the silicon or SOI wafer.

At block 812, a second electrical contact of the optoelectronic circuitof the wafer is created in the second planar bonding surface, the secondelectrical contact at least partially circumscribing the firstelectrical contact of the second planar bonding surface.

The first and second planar bonding surfaces of the die and wafer,respectively, are made flat enough for a direct-bonding process, by CMP,for example. The respective optical windows are direct-bonded to eachother across the bonding interface by a dielectric-to-dielectricdirect-bonding process (e.g., an oxide-to-oxide direct-bonding process),for example. The respective coplanar metal electrical contacts aredirect-bonded to each other across the bonding interface using ametal-to-metal direct-bonding process. When direct hybrid bonding (DBI®for example) is utilized, the nonmetal direct-bonding of the respectiveoptical windows may occur first. Then in an annealing step of the directhybrid bonding process, the complementary electrical contacts onopposing sides of the bonding interface are direct-bonded intometal-to-metal bonds. The nonmetal direct-bonding and then the metaldirect-bonding results in a direct-bonded optoelectronic interconnectbetween dies bearing photonic devices, such as III-V semiconductorphotonic devices, and a wafer bearing optoelectronic circuitry. Thephotonic devices may be lasers, optical diodes, photodetectors, LEDs,and so forth.

After the direct-bonded optoelectronic interconnects are formed betweendies and wafer, the wafer with instances of the dies bonded may be dicedor individuated into individual optoelectronic devices, or into groupsof optoelectronic devices. For some applications, such as analog camerasensors, a wafer with direct-bonded bonded dies may be left undiced,with an array of the optoelectronic devices forming the grid of thecamera sensor on relatively large sections of the wafer.

The photonic devices may also be situated on their own wafer, to bedirect-bonded to another wafer bearing CMOS circuitry or otheroptoelectronic circuitry, providing a wafer-to-wafer (W2 W) process formaking mLED arrays, for example.

FIG. 9 shows an example method 900 of bonding a die that includes aphotonic device, such as a III-V semiconductor photonic device, to asilicon wafer or silicon-on-insulator (SOI) wafer to form anoptoelectronic interconnect for high-density integrated photonics. Inthe flow diagram of FIG. 9, operations of the example method 900 areshown as individual blocks.

At block 902, a first planar bonding interface is created on a diecomprising a photonic device based on a III-V semiconductor compoundwith fully-processed metal contacts.

At block 904, a second planar bonding interface is created on a siliconor SOI wafer.

At block 906, respective optical windows of the first planar bondinginterface of the die and the second planar bonding interface of thesilicon or SOI wafer are direct-bonded together to create an opticalinterconnect between the die and the silicon or SOI wafer.

At block 908, respective first electrical contacts of the first planarbonding interface of the die and the second planar bonding interface ofthe silicon or SOI wafer are direct-bonded together to create a firstelectrical interconnect between the die and the silicon or SOI wafer.

At block 910, respective second electrical contacts of the first planarbonding interface of the die and the second planar bonding interface ofthe silicon wafer or wafer are direct-bonded together to create a secondelectrical interconnect between the die and the silicon or SOI wafer.

The coplanar optical windows, first electrodes, and second electrodesenable a direct-bonding operation, such as direct hybrid bonding (DBI®for example) to bond both the optical path and the electrical paths inthe combined optoelectronic interconnect formed thereby. There is onlyone planar bonding interface for both optical and electricalinterconnects to be created in one bonding operation. The combinedoptical and electrical interconnect enables high-density integration ofphotonics into microelectronic packages, because the adhesive-freedielectric-to-dielectric bonding and the solder-free metal-to-metalbonding employed can create high-density electrical interconnects on thesame bonding interface as the bonded optical interconnect. Since theoptoelectronic dies may be fully-processed to begin with,known-good-dies may be used, which is not possible conventionally. Sincethe optoelectronic dies begin as fully-processed components,photolithography over their top surfaces can scale to high density.

In the specification and following claims: the terms “connect,”“connection,” “connected,” “in connection with,” and “connecting,” areused to mean “in direct connection with” or “in connection with via oneor more elements.” The terms “couple,” “coupling,” “coupled,” “coupledtogether,” and “coupled with,” are used to mean “directly coupledtogether” or “coupled together via one or more elements.”

While the present disclosure has been disclosed with respect to alimited number of embodiments, those skilled in the art, having thebenefit of this disclosure, will appreciate numerous modifications andvariations possible given the description. It is intended that theappended claims cover such modifications and variations as fall withinthe true spirit and scope of the disclosure.

1. A direct-bonded optoelectronic interconnect, comprising: a firstbonding plane of a first die or wafer comprising a first optical windowand electrical contacts of a photonic device of the first die or wafer;a second bonding plane of a second die or wafer comprising a secondoptical window and electrical contacts of the second die or wafer; andthe optical windows of the first die or wafer and the second die orwafer direct-bonded together; and the respective electrical contacts ofthe first die or wafer and the second die or wafer direct-bondedtogether.
 2. The direct-bonded optoelectronic interconnect of claim 1,wherein the electrical contacts of the first die or wafer at leastpartially circumscribe the first optical window of the first die orwafer, or the electrical contacts of the second die or wafer at leastpartially circumscribe the second optical window of the second die orwafer.
 3. The direct-bonded optoelectronic interconnect of claim 1,wherein the first optical window and the second optical window aredirect-bonded together by a dielectric-to-dielectric direct bond withouta separate adhesive, or by a direct bond of a direct hybrid bondingoperation; and wherein the electrical contacts of the first die and theelectrical contacts of the second die are direct-bonded together by ametal-to-metal direct-bond, or by a direct bond of the direct hybridbonding operation.
 4. The direct-bonded optoelectronic interconnect ofclaim 1, further comprising: a first bonding plane associated with thefirst die comprising the first optical window, a first electricalcontact at least partially circumscribing the first optical window andcoplanar with the first optical window, and a second electrical contactat least partially circumscribing the first electrical contact andcoplanar with both the first electrical contact and the first opticalwindow; and a second bonding plane associated with the second diecomprising the second optical window, a first electrical contact of thesecond die at least partially circumscribing the second optical windowand coplanar with the second optical window, and a second electricalcontact of the second die at least partially circumscribing the firstelectrical contact of the second die and coplanar with both the firstelectrical contact of the second die and the second optical window. 5.An apparatus, comprising: a first die including an optoelectronicdevice; an optical coupling area of the first die in opticalcommunication with the optoelectronic device; a coupling plane of thefirst die for optically and electrically coupling with a complementarycoupling plane of a second die, a part of the coupling plane of thefirst die containing the optical coupling area of the first die; a firstelectrical contact of the optoelectronic device disposed outside aperimeter of the optical coupling area in the coupling plane of thefirst die; and a second electrical contact of the optoelectronic devicedisposed outside a perimeter of the first electrical contact in thecoupling plane of the first die.
 6. The apparatus of claim 5, whereinthe first electrical contact completely surrounds the optical couplingarea in the coupling plane of the first die; and wherein the firstelectrical contact of the optoelectronic device of the first die isdisposed outside a perimeter of an optical coupling area of a siliconwaveguide of the second die.
 7. The apparatus of claim 5, furthercomprising: a second die, wherein the first die is capable of opticallyand electrically coupling with the second die upon joining respectivecoupling planes of the first die and the second die; a silicon waveguidein the second die, the silicon waveguide in optical communication withan optical coupling area of the second die; the optical coupling area ofthe second die occupying a part of the coupling plane of the second die;an optoelectronic circuit of the second die; a first electrical contactof the optoelectronic circuit disposed outside a perimeter of theoptical coupling area of the second die in the coupling plane of thesecond die, the first electrical contact of the optoelectronic circuitmatching a planar geometric profile of the first electrical contact ofthe first die; and a second electrical contact of the optoelectroniccircuit disposed outside a perimeter of the first electrical contact ofthe optoelectronic circuit in the coupling plane of the second die, thesecond electrical contact of the optoelectronic circuit matching aplanar geometric profile of the second electrical contact of the firstdie.
 8. The apparatus of claim 7, wherein an electrical routing from theoptoelectronic circuit of the second die to the first and secondelectrical contacts of the optoelectronic circuit is within the couplingplane of the second die.
 9. The apparatus of claim 8, wherein the secondelectrical contact of the optoelectronic circuit comprises an open-loopor a discontinuous trace within the coupling plane of the second die,further comprising a gap in the open-loop of the discontinuous trace foraccommodating the electrical routing to the first electrical contact ofthe optoelectronic circuit within the coupling plane of the second die.10. The apparatus of claim 7, wherein the optical coupling area of thesecond die includes at least a grating surface for an optical mode-matchcoupling between the first die and the second die.
 11. The apparatus ofclaim 10, wherein the grating surface is less than 10 microns (μ) thickfor single mode infrared transmission.
 12. The apparatus of claim 5,wherein the first die has fully-processed electrodes of theoptoelectronic device and fully-processed first and second electricalcontacts of the optoelectronic device before joining to the second die.13. The apparatus of claim 5, further comprising: an optical couplebetween the optical coupling area of the first die and the opticalcoupling area of the second die in a joined coupling plane; ametal-to-metal bond or a direct hybrid bond between the first electricalcontact of the optoelectronic device of the first die and the firstelectrical contact of the optoelectronic circuit of the second die inthe joined coupling plane; and a metal-to-metal bond or a direct hybridbond between the second electrical contact of the optoelectronic deviceof the first die and the second electrical contact of the optoelectroniccircuit of the second die in the joined coupling plane.
 14. Theapparatus of claim 13, further comprising a transparent conductive oxide(TCO) between a III-V compound semiconductor and the silicon waveguideto enhance electrical conductivity into the III-V compound semiconductorand to enhance a uniformity of the electrical conductivity.
 15. Theapparatus of claim 14, wherein the transparent conductive oxide (TCO) isselected from the group consisting of aluminum doped zinc oxide (AZO),gallium doped zinc oxide (GZO), and indium tin oxide (ITO).
 16. Theapparatus of claim 5, further comprising a bottom surface of a III-Vcompound semiconductor roughened by etching to reduce a reflection loss.17. The apparatus of claim 5, further comprising a dielectric materialbetween the bottom surface of a III-V compound semiconductor and thesilicon waveguide to reduce a reflection loss between the III-V compoundsemiconductor and the silicon waveguide, wherein the dielectric materialhas a refractive index between the index of refraction of the siliconand the index of refraction of the III-V compound semiconductor.
 18. Theapparatus of claim 17, wherein an optical thickness between the bottomsurface of the III-V compound semiconductor and a top surface of thesilicon waveguide is an odd multiple of one-quarter of the wavelength ofan operative light of the apparatus.
 19. The apparatus of claim 18,further comprising a reflective layer on top of the optoelectronicdevice of the first die on the surface opposite to the bond surface. 20.An electrical and optical interconnect for high-density integratedphotonics, comprising: a first coupling plane formed on a side of afirst die; a first optical window formed in the coupling plane of thefirst die; a first electrical contact outside a perimeter of the firstoptical window and disposed in the coupling plane of the first die; anda second electrical contact outside a perimeter of the first electricalcontact and disposed in the coupling plane of the first die.
 21. Theelectrical and optical interconnect for high-density integratedphotonics of claim 20, further comprising: a second coupling planeformed on a second die; a second optical window in the coupling plane ofthe second die; a first complementary electrical contact outside aperimeter of the second optical window and disposed in the couplingplane of the second die; a second complementary electrical contactoutside a perimeter of the first complementary electrical contact anddisposed in the coupling plane of the second die; and electrical leadsto the first complementary electrical contact and the secondcomplementary electrical contact disposed in the coupling plane of thesecond die.
 22. The electrical and optical interconnect for high-densityintegrated photonics of claim 20, wherein the first electrical contactof the first die and the first complementary electrical contact of thesecond die each comprise a square, rectangular, circular, or ovalineconductive line surrounding respective first or second optical windows.23. The electrical and optical interconnect for high-density integratedphotonics of claim 20, further comprising a dielectric-to-dielectricoptical interconnect between the first optical window of the first dieand the second optical window of the second die, and a solderlessmetal-to-metal bonded electrical interconnect or a direct hybrid bondedinterconnect between the first and second electrical contacts of thefirst die and the first and second complementary electrical contacts ofthe second die forming high-density electrical interconnects on joinedcoupling planes of the first die and the second die.